Improve chassis rigidity on Cab ?

[Deschodt]

Let me start with a side note, only today (3y after buying the car) did I notice the steering wheel is angled on these cars !!! With hands at 9-3 sitting straight, the 9AM hand is about 1/2" further away than the 3PM hand - LOL (measured with a USB cable from my chin!!!). Designed that way I imagine, took me that long to notice. Wow!

Anyway - Is there a proven way to reduce the chassis jiggling over irregular tarmac ? It feels really awful on the cabrio especially, like disconnected... Any sort of extra bracing F to R ?
I replaced the suspension and had the rear subframe mounts welded - not it - I'm still on 19s and seriously considering 18s for less squeaks and movement.. Anyone confirming 18s are a worthy option overall ?

Side note: the cab top used to squeak sooo much on those imperfections but no more - the solution was *not* the ever recommended Gummi plfledge but instead graphite powder. Silent windows now ! Slightly dirty after application, but quiet !!! graphite for the win !

[lmtfi]

I doubt you have a chassis problem. It sounds like you have a suspension choice, suspension settings and 19" wheel combined problem. You already know that the 19" wheel with low profiles is going to transfer more road imperfections to the suspension to manage. Then its a function of shock and spring choices (you didn't note your set-up). If you want a smoother, quieter and more forgiving ride - those priorities move you away from the firm/responsive suspension choices many go with. Also, tire choice affects NVH.

[bosundave]

Let me start with a side note, only today (3y after buying the car) did I notice the steering wheel is angled on these cars !!! With hands at 9-3 sitting straight, the 9AM hand is about 1/2" further away than the 3PM hand - LOL (measured with a USB cable from my chin!!!). Designed that way I imagine, took me that long to notice. Wow!

Anyway - Is there a proven way to reduce the chassis jiggling over irregular tarmac ? It feels really awful on the cabrio especially, like disconnected... Any sort of extra bracing F to R ?
I replaced the suspension and had the rear subframe mounts welded - not it - I'm still on 19s and seriously considering 18s for less squeaks and movement.. Anyone confirming 18s are a worthy option overall ?

Side note: the cab top used to squeak sooo much on those imperfections but no more - the solution was *not* the ever recommended Gummi plfledge but instead graphite powder. Silent windows now ! Slightly dirty after application, but quiet !!! graphite for the win !

Our verts will ALWAYS creak and squeak. This is mitigated not with Gummi (I use that too) but with a pricey product called Genuine BMW Carbaflo Ksp 105 Lubricant - 50G. BUY IT!!!!. (eBay/Turner etc)Use it. It works for months before you need to re apply it.
I am getting a whats called a half roll bar cage welded in place more or less permanently. That way I can also use my neat aftermarket seats since I will have to use a HARNESS which I can anchor to the roll bar. It will stiffen up my car SIGNIFICANTLY. They make specific roll cages that fit our verts. The top will go up and down no problem.

Loose the 19's. I run FOUR D-Force 18x9.5" wheels with four 265/35-18 tires. Get the Gloss black with the machined lip. Have your painter match your body color on the lip portion. The gloss black cleans easily and wont show brake dust as much. These are ultra light racing wheels that are MORE than strong to run in the street.I have for over 10 years!

They will only bend if you jump an 18" curb. Ask me how I know. They can be easily straightened for $80 to $100 in case you totally screw up like I did in a very bad FLOOD (could not see this curb), My wheels are wheels are 10 years old and as good as new.

Adjust your tire pressure so all four get to around 40 psi when run at triple digit speeds. My front 265mm tires do NOT tramline. I use as close to factory alignment ON or OFF the track. A little TOE IN front and rear gives you your best high speed stability.

If you run coil overs do NOT slam your car. Run it has high as you can. It will still be plenty low. FULL caster and -1.5 to -2.0 camber front. -1.5 camber rear. Factory toe in.
Use any good brand adjustable LINKS for your front sway bar. Google how to set the length.

Now, buy a 30mm adjustable front anti sway bar. They say do NOT replace the rear bar. I did, not knowing. It does seem to handle awesome on or off the track. I got the Turner pair made by H&R. I have the front set at full stiff and the rear at full soft.
For the street, Achilles, Vredestein or even Atlas are dandy. Federal are too noisy. Good tires, but noisy tread pattern. Achilles(Thailand) suffers a supply chain issue since Covid. But they are my first choice.

Use no spacers in front. I run 20mm spacers in the rear. The wheels say use 12.5mm. Not enough IMO use 20mm spares that come with the correct length(longer) lug bolts for our cars. I use cheap Amazon spacers with a good dose of anti-seeze on the spacers, not the lug bolts.

Your car will be 100% transformed to what should have rolled off the assembly line, but did not.
STOP using graphite powder!!!! You CAN and should use a polymer on you windows to make them run smoother.
Rejex Polymer Protectant Wax Finish by Corrosion Technologies - 12 oz - 61001.....lasts forever. Less than $20. Good stuff.

KEEP using Gummi on your rubber seals and 303 uv protectant spray on ALL plastics and your leather, including your steering wheel. NO silicone. Dries completely. You can even spry your belts and tire treads with it.